1. Field of the Invention
The present invention relates to a discharge flow control system and method of a hydraulic pump in hydraulic equipment such as excavator, loader, dozer, crane, etc., and more particularly to a discharge flow control system and method to make the hydraulic pump to discharge a fairly precise mount of flow required for a desired work
2. Decription of Prior Arts
In recent years, with the developement of electronic control unit such as microprocessors, the hydraulic system, particularly in heavy construction equipment, incorporates the electronic devices for automation.
The fundamental technologies required in the automation of construction equipment such as excavator include a position control technology for various moving parts, and an energy minimization technology for preventing flow loss.
The most general way which has been used for the enhancement of the operation efficiency of equipment and for the precise position control is to compare the flow amount required by an operator with the tilt angle data of the swash plate in hydraulic pump by a tilt angle detecting means, and compensate for errors therebetween.
FIG. 1 shows a schematic diagram of hydraulic system in a conventional excavator.
As shown in FIG. 1, the hydraulic system has an engine 1 which serves as a power source, two variable displacement pumps 2 and 3 and an auxilliary pump 4 for discharging a constant amount of operating oil, two pump regulators 5 and 6 for controlling each pump by moving each swash plate in pumps 2 and 3, solenoid controlled proportional valves 7 and 8 for pumps 2. and 3 to generate a pilot pressure proportional to an input signal by the operating oil supplied from auxilliary pump 4 and to provide the pilot pressure to pump regulators 5 and 6, at least one or more hydraulic actuators 9, 10 and 11 which are driven by a discharge flow of pumps 2 and 3, a flow control valve 12 to control the direction and the amount of flow between actuators 9, 10 and 11 and pumps 2 and 3 by the displacement of a spool therein, and a solenoid controlled proportional valve 13 generating a pilot pressure for flow control valve 12.
However, the conventional system described above has the drawbacks that a frequent operation error occurs due to hysterisis characteristics of the solenoid controlled proportional valves, and that a precise control of the discharge flow amount is difficult due to the variable efficiency of the pumps.